U.S. patent number 7,681,645 [Application Number 11/713,062] was granted by the patent office on 2010-03-23 for system and method for stimulating multiple production zones in a wellbore.
This patent grant is currently assigned to BJ Services Company. Invention is credited to Bobby Frank McMillin, Avel Z. Ortiz, Mark Zimmerman.
United States Patent |
7,681,645 |
McMillin , et al. |
March 23, 2010 |
System and method for stimulating multiple production zones in a
wellbore
Abstract
A system and method for selectively stimulating a plurality of
producing zones of a wellbore in oil and gas wells, the system
being cemented within the wellbore. The system includes a plurality
of modules connected in a string wherein the modules can be
selectively actuated to stimulate producing zones adjacent the
modules. Each module includes a sleeve shiftable between a closed
position and a treating position where a plurality of radial
passageways are exposed to the central passageway of the assembly.
The system includes a wiper plug that is adapted to pass through
ball seats of various sizes in the plurality of modules and an acid
solution pumped into the string to break down the cement at the
producing zones. The system may include at least one natural rubber
wiper ball to remove residual cement from the string.
Inventors: |
McMillin; Bobby Frank (Katy,
TX), Ortiz; Avel Z. (Houston, TX), Zimmerman; Mark
(Cypress, TX) |
Assignee: |
BJ Services Company (Houston,
TX)
|
Family
ID: |
39721852 |
Appl.
No.: |
11/713,062 |
Filed: |
March 1, 2007 |
Prior Publication Data
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|
|
|
Document
Identifier |
Publication Date |
|
US 20080210429 A1 |
Sep 4, 2008 |
|
Current U.S.
Class: |
166/291;
166/307 |
Current CPC
Class: |
E21B
33/13 (20130101); E21B 34/14 (20130101); E21B
43/261 (20130101); E21B 43/14 (20130101) |
Current International
Class: |
E21B
34/00 (20060101) |
Field of
Search: |
;166/285,291,306,307,177.4 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
International Search Report and Written Opinion dated Sep. 24,
2008, for corresponding PCT Application No. PCT/US2008/055464.
cited by other.
|
Primary Examiner: Neuder; William P
Attorney, Agent or Firm: Zarian Midgley & Johnson
PLLC
Claims
What is claimed is:
1. A method for selectively stimulating a plurality of producing
zones in an oil and gas well comprising: positioning an assembly in
the well, the assembly comprising a plurality of modules connected
to a string, wherein each module is positioned adjacent a zone to
be stimulated and each module includes a housing having a central
passageway, one or more passageways extending radially through the
housing, and a shiftable sleeve slidably mounted within the
housing, wherein the shiftable sleeve is adapted to receive an
actuating ball for shifting the shiftable sleeve from a closed
position over the radial passageways to an open position whereby
the radial passageways are in communication with the central
passageway of the housing; pumping cement down the string and into
an annulus between the string and the wellbore; pumping a wiper
plug down the string; pumping an acid solution down the string,
wherein the acid solution is pumped down the string prior to the
curing of the cement; allowing the cement in the annulus to cure;
selectively breaking down the cured cement and stimulating each of
the producing zones in succession from the lowermost zone to the
uppermost zone from the module adjacent each zone by successively
moving the shiftable sleeve to the open position in each of the
modules beginning with the lowermost module and finishing with the
uppermost module by using a progressively larger actuating ball for
each of the successive modules.
2. The method of claim 1 further comprising pumping at least one
wiper ball down the string.
3. The method of claim 2 wherein the at least one wiper ball is
pumped down the string within a spacer fluid.
4. The method of claim 2 wherein the at least one wiper ball is a
natural rubber wiper ball.
5. The method of claim 1 wherein the acid solution pumped down the
string is acetic acid.
6. The method of claim 1 wherein the wiper plug is a flexible wiper
plug.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates an improved system and
method for stimulating multiple production zones in a wellbore.
U.S. Pat. No. 6,006,838 discloses a string that includes modules
with sliding sleeves that may be used to stimulate multiple
production zones in a wellbore in a single trip into the wellbore.
The present invention discloses positioning the string disclosed in
U.S. Pat. No. 6,006,838 within a desired location within a wellbore
and then cementing the string in place using an acid soluble
cement. Cement is pumped down the string, out the end of the
string, and up and around the outside of the diameter of the
string. The cement is allowed to cure cementing the string at the
desired location.
A wiper plug is pumped down the string after the cement, and
preferably before the displacement fluid, to wipe any residual
cement from the inner diameter of the string. The wiper plug also
helps to separate the acid soluble cement from acid pumped down the
string after the wiper plug. At least one wiper ball may also be
pumped down the string after the wiper plug. The wiper ball may be
pumped down the string within a spacer fluid to help protect the
wiper ball from being damaged by the acid solution. The wiper ball
may help to remove any residual cement from the internal bores of
the modules allowing the sliding sleeves to slide when actuated.
The acid pumped within the string also prevents any residual cement
from curing inside of the string.
After the cement has cured around the outside of the string, fluid
is pumped down the string. The hydraulic pressure of the pumped
fluid moves the sliding sleeve of the lowermost module to an open
position. The acid within the string breaks down the cement around
the string after the sliding sleeve of a module is opened.
Hydraulic pressure may then fracture the formation adjacent the
opened module. A proppant containing slurry may follow behind the
acid to extend and support the fracture. Once the formation has
been fractured an appropriately sized ball may be dropped down the
string to land in the ball seat of the next lowermost module. The
seated ball prevents flow to the first module and the pressure
within the string will build until the sliding sleeve of the second
module moves to the open position. The acid then breaks down the
cement adjacent to the second module and hydraulic pressure may
fracture the formation at this location. The process is repeated
until cement adjacent each module has been broken down and each of
the specified zones have been fractured.
2. Description of the Related Art
This present invention relates to an improved system and method for
stimulating producing zones of an openhole wellbore in oil and gas
wells. Previously disclosed was an assembly for selectively
stimulating a wellbore without the use of openhole inflatable
packers. This assembly is especially suited to perform a
combination of matrix acidizing jobs and near wellbore erosion jobs
at a number of producing zones in the wellbore in a single
trip.
Prior to the disclosed assembly, operators who were interested in
stimulating multiple producing zones in an openhole wellbore could
stimulate the zones one zone at a time by using a workstring and an
openhole inflatable packer. Such a method and assembly required the
operator to set an inflatable packer (or other similar apparatus)
above each zone of interest to be stimulated and then, following
the stimulation job, to release the packer (or packers) and trip
the packer assembly to a new location where it would be reset for
the next stimulation job. This procedure would be repeated for each
desired zone of interest. However, because of the tripping time and
the difficulty in setting and maintaining the seal in inflatable
packers in openhole wellbores, such a method was both time
consuming and relatively unreliable. Furthermore, openhole
inflatable packers (or other similar devices) are expensive to rent
or to purchase. As a result of the relative unreliability and cost
of using openhole inflatable packers, such assemblies prove to be
uneconomical in marginal fields such as fields in the Permian Basin
region of West Texas and Eastern New Mexico.
The previously disclosed assembly does not require an inflatable
packer and is very economical to build and maintain. Thus, an
operator can use the assembly for a small incremental cost over
what it costs to perform an acid job and receives the benefits of
not only a matrix acidizing treatment, but can also enhance the
flow in the near wellbore region by eroding away near wellbore skin
damage. The assembly also allows an operator to accurately position
an assembly in a wellbore to ensure that the producing zones of
interest are stimulated.
The present invention is an improvement to the previously disclosed
assembly for selectively stimulating a wellbore without the use of
openhole inflatable packers. Specifically, the system and method is
disclosed for cementing the assembly at a desired location within
the wellbore. The use of an acid soluble cement pumped down the
string of the assembly allows the assembly to be cemented in place
within a wellbore. The use of a wipe plug and at least one wiper
ball removes any residual cement from the inside of the string. The
acid soluble cement also provides that the use of an acid within
the string prevents the curing of any residual cement within the
string.
SUMMARY OF THE INVENTION
One embodiment of the present invention is directed to a system for
selectively stimulating a plurality of producing zones in an oil
and gas well comprising a string cemented into a wellbore, a
plurality of modules spaced in the string at predetermined
locations, wherein each module comprises a housing having a central
passageway therethrough, a plurality of passageways extending
radially through the housing, and a shifting sleeve slidably
mounted within the housing wherein the shifting sleeve is moveable
from a closed position over the radial passageways to an open
position whereby the radial passageways are in communication with
the central passageway of the housing and wherein the shifting
sleeve includes a ball seat for receiving an actuating ball for
shifting the shifting sleeve from the closed position to the open
position. The lowermost module in the assembly is adapted to
receive an actuating ball and each successive module in the
assembly is adapted to receive a larger actuating ball than the
module immediately below it. The size of the ball seat will differ
from module to module with the lowermost module having the smallest
ball seat and each successive module in the assembly will have a
larger ball seat than the module immediately below it. Each of the
radial passageways may include a jet nozzle.
Cement may be pumped down the string to cement the string within
the wellbore at the desired location. A wiper plug may be pumped
down the string after the cement to wipe residual cement from the
string. The wiper plug may also help to separate the cement from
the displacement fluid pumped down the string after the cement. The
wiper plug may be adapted to pass through varying sizes of ball
seats found in the modules of the string.
The cement used may be an acid soluble cement and the fluid pumped
after the wiper plug may be an acid solution which prevents any
residual cement from curing inside of the string. A wiper ball,
which may be comprised of rubber, may be pumped down the string
after the wiper plug. The wiper ball may be comprised of a natural
or synthetic rubber as would be appreciated by one of ordinary
skill in the art having the benefit of this disclosure. The wiper
ball may also help remove any residual cement from the inside of
the string. The wiper ball may be pumped within a spacer fluid to
prevent the acid solution from damaging the wiper ball. The acid
solution may be pumped down the string to fill the string above the
uppermost module to prevent the curing of any residual cement
inside of the string while the cement ori the exterior of the
string is allowed to cure and set the string within the wellbore.
The acid solution may be acetic acid or other acid solutions as
would be appreciated by one of ordinary skill in the art having the
benefit of this disclosure.
In another embodiment, the housing may include an interchangeable
nozzle body wherein the passageways extend radially through the
nozzle body. The housing may further comprise a top sub connected
to the upper end of the nozzle body and a bottom sub connected to
the lower end of the nozzle body.
Each module may further comprise one or more radially extending
flow ports in the shifting sleeve beneath the ball seat which
communicates with one or more flow ports in the housing when the
shifting sleeve is in the open position.
Another embodiment of the present invention is directed to a system
for selectively stimulating a plurality of producing zones in an
oil and gas well comprising a plurality of modules connected in a
string that is cemented within a wellbore. Each module comprises a
housing having a central passageway therethrough, one or more
passageways extending radially through the housing, and a shiftable
sleeve mounted in the central passageway of the module, wherein the
shiftable sleeve is moveable from a closed position over the radial
passageways to an open position whereby the radial passageways are
in communication with the central passageway of the housing, and
wherein the shiftable sleeve is adapted to receive an actuating
means for shifting the shiftable sleeve from the closed position to
the open position. The actuating means may include balls, darts,
bars, plugs or similar devices.
One embodiment of the present invention is a method for selectively
stimulating a plurality of producing zones in an oil and gas well.
The method includes positioning an assembly in the well, the
assembly comprising a plurality of modules connected to a string,
wherein each module is positioned adjacent a producing zone to be
stimulated and each module includes a housing having a central
passageway, one or more passageways extending radially through the
housing, and a shiftable sleeve slidably mounted within the
housing, wherein the shiftable sleeve is adapted to receive an
actuating ball for shifting the shiftable sleeve from a closed
position over the radial passageways to an open position whereby
the radial passageways are in communication with the central
passageway of the housing.
The method further includes pumping cement down the string until
the cement exits the end of the string and fills an annulus between
the string and the wellbore and also pumping a wiper plug down the
string. The method also includes pumping an acid solution down the
string and allowing the cement in the annulus to cure. Once the
cement in the annulus or exterior of the string has cured, the
method includes selectively breaking down the cured cement and
stimulating each of the producing zones in succession from the
lowermost zone to the uppermost zone from the module adjacent each
zone by successively moving the shiftable sleeve to the open
position in each of the modules beginning with the lowermost module
and finishing with the uppermost module by using a progressively
larger actuating ball for each of the successive modules.
The method may further include pumping at least one wiper ball down
the string. The wiper ball may be a natural rubber wiper ball and
may be pumped down the string within a spacer fluid.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a partial cutaway of an assembly for selectively
stimulating a plurality of producing zones in an openhole
wellbore.
FIG. 2 shows a partial cutaway of one embodiment of a module used
in the assembly shown in FIG. 1.
FIG. 3 illustrates the module of FIG. 2 with the shifting sleeve in
the open position.
FIG. 4 shows a partial cutaway of an alternative embodiment of a
module for use in an assembly for selectively stimulating a
plurality of producing zones in a wellbore.
FIG. 5 illustrates a partial cutaway of a system that may be
cemented in a wellbore and used for selectively stimulating a
plurality of producing zones in an openhole wellbore.
FIG. 6 illustrates a partial cutaway system for selectively
stimulating a plurality of producing zones, the system being
cemented within the wellbore.
While the invention is susceptible to various modifications and
alternative forms, specific embodiments have been shown by way of
example in the drawings and will be described in detail herein.
However, it should be understood that the invention is not intended
to be limited to the particular forms disclosed. Rather, the
intention is to cover all modifications, equivalents and
alternatives falling within the spirit and scope of the invention
as defined by the appended claims.
DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
Illustrative embodiments of the invention are described below as
they might be employed in a method and system for selectively
simulating multiple production zones or intervals within a
subterranean oil or gas well, the system being cemented within the
well. Persons of ordinary skill in the art, having the benefit of
the present disclosure, will recognize that the teachings of the
present disclosure will find application in any number of
alternative embodiments employing the general teachings of the
illustrative embodiments. In the interest of clarity, not all
features of an actual implementation are described in this
specification. It will of course be appreciated that in the
development of any such actual embodiment, numerous
implementation-specific decisions must be made to achieve the
developers' specific goals, such as compliance with system-related
and business-related constraints, which will vary from one
implementation to another. Moreover, it will be appreciated that
such a development effort might be complex and time-consuming, but
would nevertheless be a routine undertaking for those of ordinary
skill in the art having the benefit of this disclosure.
Further aspects and advantages of the various embodiments of the
invention will become apparent from consideration of the following
description and drawings.
Referring to FIGS. 1-3, a preferred embodiment of an assembly for
selectively stimulating producing zones in a subterranean wellbore
will now be described. The assembly 1 includes a plurality of
modules which are attached to a tailpipe 4 (shown in cutaway to
reflect the longitudinal distance between the modules). The
assembly in FIG. 1 includes modules 5, 10, 15 and 20. Tailpipe 4 is
suspended from service packer 3 which is set inside casing 6, above
the openhole wellbore 2. The service packer may be, for example, a
compression packer, such as an SD-1 or MR1220 packer available from
BJ Services Company. A workstring of tubing, drillpipe or the like
extends from packer 3 to the surface. The tailpipe string, being
suspended from packer 3, extends into the openhole beneath the
casing shoe. In a preferred embodiment, modules 5, 10, 15 and 20
are spaced in the tailpipe string at predetermined locations so
that an individual module is adjacent a producing zone desired to
be stimulated. The tailpipe string may be comprised of tubing,
drillpipe or the like and the length of tailpipe between adjacent
modules will depend on the distance between the producing zones or
targets of interest. Alternatively, it will be understood that the
packer could be reset at different locations in the casing to
locate one or more modules of the assembly adjacent one or more
producing zones or targets of interest. In other words, the entire
assembly can be repositioned within the wellbore to more accurately
position some of the modules without tripping the assembly out of
the wellbore.
As shown in FIG. 2, each module comprises a generally
tubular-shaped housing 21 which includes a threaded upper and lower
end for connecting the module to the tailpipe string. Central
passageway 25 extends longitudinally through housing 21. Each
module includes shifting sleeve 22 which is adapted for
longitudinal movement along the inner wall of housing 21. Shifting
sleeve 22 includes one or more radially extending ports 28 which
are arranged about the circumference of the sleeve. Housing 21 also
includes one or more radially extending ports 27 circumferentially
spaced about the housing. The number of ports 28 in shifting sleeve
22 will correspond to the number of flow ports 27 in housing 21.
Shifting sleeve 22 includes a landing seat or ball seat 35. The
size of ball seat 35 will differ from module to module in the
assembly, with the lowermost module 20 having the smallest ball
seat and the uppermost module 5 having the largest ball seat.
Housing 21 may include a plurality of nozzle holes 23 which extend
radially through the wall of housing 21 for receiving
interchangeable jet nozzles 24. Jet nozzles 24 may be held in
nozzle holes 23 by any suitable means such as mating threads, snap
rings, welding or the like. Jet nozzles may come in a wide variety
of orifice sizes. The size of the nozzle orifice may be
predetermined to achieve the desired fluid hydraulics for a
particular acid job. Some of the nozzles may be selectively blanked
off to achieve the optimum flow rates and pressure drops across the
remaining nozzles. In general, the number and size of the working
jet nozzles will reflect the desired kinetic energy to be used in
treating a given producing zone.
Shifting sleeve 22 is initially attached to housing 21 in the
closed position by one or more shear screws 30 so that the shifting
sleeve straddles jet holes 23, jet nozzles 24 and fluid flow ports
27. Seals 32 seal the annular space between shifting sleeve 22 and
housing 21. Elastomeric seals 32 may be o-ring seals, molded seals
or other commonly used oilfield seals. The remaining components of
the module may be manufactured from common oilfield materials,
including various steel alloys.
As shown in FIG. 3, centralizing coupling 40 may be attached to the
lowermost end of housing 21. Centralizing coupling 40 not only
connects the module to lower tailpipe 4 but also centralizes the
module and assembly in the wellbore. Centralizing coupling 40
includes a plurality of centralizing ribs, with adjacent fluid flow
passageways therebetween.
As shown in FIG. 1, an assembly for selectively stimulating a
plurality of intervals or targets in a wellbore includes a
plurality of modules assembled in a tailpipe string. By varying the
length of tailpipe between modules, an operator can space the
individual modules so that a module is adjacent each desired
producing interval or target to be stimulated. The selectivity is
provided by varying the size of the landing seat 35 on shifting
sleeve 22. The lowermost module 20 will have the smallest ball seat
35, i.e., the smallest internal diameter of any of the modules, for
catching the smallest ball. The next to last module in the assembly
will have a slightly larger ball seat 35 and so on until the
uppermost module, which will have the largest ball seat, i.e., the
largest internal diameter of any of the modules. Thus, the
actuating balls for the assembly will increase in diameter as one
moves from the lowermost module to the uppermost module.
In operation, the assembly of FIG. 1 is run into the wellbore
suspended from packer 3. The packer is set in the production casing
near the casing shoe at a predetermined location. Tailpipe 4 and
modules 5, 10, 15 and 20 extend beneath the casing shoe into the
open hole. The modules are spaced apart in the tailpipe string so
that each particular module will be adjacent to a producing zone
that the operator desires to stimulate. The stimulation treatment
begins with the lowermost zone and works its way up the wellbore.
An appropriate sized ball is dropped or pumped down the workstring
and into the assembly until it lands on seat 35 of shifting sleeve
22 in the lowermost module 20. Pressure is increased inside the
work string and assembly until the force acting across the
actuating ball and ball seat exceeds the shear value for shear
screw 30. Once shear screw 30 is sheared, shifting sleeve 22 is
shifted downward to the treating position against shoulder 42 of
housing 21. As shown in FIG. 3, when the shifting sleeve is in the
open or treating position, jet nozzles 24 are in communication with
central passageway 25. Once landed, ball 37 prevents acid from
passing out the bottom of the assembly. Acid is then pumped at a
desired rate through jet nozzles 24 to acidize and erode the
wellbore adjacent the jet nozzles. The kinetic energy created by
pumping the acid through the jet nozzles mechanically erodes away
the wellbore formation adjacent the nozzles as illustrated in FIG.
3.
Upon completion of the acid stimulation treatment of the lowermost
zone or target, a slightly larger ball is dropped or pumped down
the workstring into the assembly where it passes through the upper
modules and lands on the ball seat of module 15. Pressure is again
increased inside the workstring to shift the shifting sleeve from
the closed position to the open position so that the jet nozzles of
module 15 are exposed. Acid is then pumped through the jet nozzle
of module 15 to acidize and erode the wellbore adjacent the module.
The ball in module 15 prevents acid from flowing down to module
20.
The remainder of the zones of interest or targets are selectively
acidized or treated by dropping or pumping successively larger
balls into the assembly and repeating the above-described sequence.
Upon completion of the stimulation treatment of all zones, the
packer can be released from the production casing and the assembly
can be pulled out of the well.
The assembly allows an operator to selectively stimulate a number
of producing zones in a wellbore in a single trip. By dropping
successively larger actuating balls, an operator can shift a sleeve
in successive modules and then squeeze and jet a desired volume of
hydrochloric acid or other type of acid into the producing zones of
the interest. By diverting the acid through the nozzles in the
modules, the acid will impact the wellbore at high velocity under
squeezed pressures. The kinetic energy of the acid will erode away
the wellbore and thereby create a cavern in addition to penetrating
the formation rock with the acid. The acidizing and wellbore
erosion will enhance the ability of oil or other hydrocarbons to
flow into the wellbore at these locations. The wellbore is thus
treated both mechanically and chemically by dissolving materials
that are plugging the pores of the formation rock, such as fines,
paraffins, or clays or other materials that have reduced the
porosity and/or permeability of the formation. By jetting a large
govern at the face of the wellbore, the resistance to the flow of
oil or gas into the wellbore is reduced. Although not limited to
such application, the present invention is well suited for
stimulating a calcareous formation with, for example, hydrochloric
acid.
An alternative embodiment of a module for use in an assembly of the
present invention is shown in FIG. 4. The module has a generally
tubular shaped housing 51 comprising top sub 45, nozzle body 42,
and bottom sub 44. Central passageway 51a extends longitudinally
through the module. The upper portion of top sub 45 includes
internal threads for connecting the module to upper tailpipe 4. Top
sub 45 includes external threads on its lower end for connecting
top sub 45 to nozzle body 42. Nozzle body 42 includes internal
threads for mating with the external threads of top sub 45. Nozzle
body 42 also includes external threads on its lowermost end for
mating with internal threads on the upper end of bottom sub 44.
Bottom sub 44 includes threads on its lowermost end for mating with
internal threads on centralizing coupling 40. Centralizing coupling
40 is threadedly attached to the lower tailpipe 4.
Nozzle body 42 may be further secured to top sub 45 by one or more
set screws 52. Similarly, nozzle body 42 may be further secured to
bottom sub 44 by one or more set screws 53. Nozzle body 42 has a
plurality of radially extending nozzle ports 58 drilled
therethrough. The nozzle ports 58 extend about the circumference of
nozzle body 42. The number and size of nozzle ports 58 may vary
from module to module depending on the fluid flow characteristics
required for the stimulation treatment at each desired producing
zone. By way of example, nozzle body 42 may include eight nozzle
ports ranging in diameter from 1/16 to 3/16 of an inch spaced
approximately 45 degrees apart about the circumference of the
nozzle body.
Shifting sleeve 46 is adapted for longitudinal movement along the
inner wall of housing 51. Sleeve 46 includes one or more radially
extending flow ports 50. The annular space between shifting sleeve
46 and the inner walls of top sub 45, nozzle body 42, and bottom
sub 44 is sealed by a plurality of seals 54. Sleeve 46 is shifted
from a closed position straddling nozzle ports 58 to the
stimulating position shown in FIG. 4 by landing an appropriately
sized shifting ball (not shown) on ball seat 60. Sleeve 46 is
initially held in the closed position by one or more shear screws
48. After a shifting ball lands on seat 60 (not shown), the tubular
pressure is increased until shear screws 48 shear allowing shifting
sleeve 46 to be longitudinally moved downward to the stimulating
position. Shoulder 62 may be provided to stop the downward movement
of sleeve 46. In the stimulating position, flow ports 50 are
aligned with a corresponding number of flow ports 65 in bottom sub
44, as shown by the dotted line. Flow ports 65 extend radially
through the bottom sub and are spaced, for example, 45 degrees
apart from shear screws 48 along the same plane.
An operator can change the size and number of nozzle ports in a
module by using interchangeable nozzle bodies 42. The
interchangeable nozzle bodies provide an operator an alternative to
the use of interchangeable jet nozzles as described in the
embodiment of FIG. 2. Nozzle body 42 may be made of a variety of
steel alloys commonly used in the oil industry or may be made of
high chromium materials or heat treated metals to increase the
erosion resistance of nozzle ports 58. The remaining portions of
the module, including top sub 45, bottom sub 44 and shifting sleeve
46, can be made of a variety of steel alloys commonly used in the
oil field.
Although different embodiments of a module are illustrated in FIGS.
2 and 4, the method of selectively actuating the different modules
of an assembly can be more readily understood by comparing the
respective ball seats of the modules in these figures. As can be
seen, the internal diameter of ball seat 60 in the module of FIG. 4
is substantially larger than the internal diameter of ball seat 35
in the module of FIG. 2. Thus, the actuating ball for seat 35 will
easily pass through ball seat 60 and continue through the assembly
until it lands on seat 35 of the lower module. Therefore, an
operator can selectively actuate the modules in the assembly from
the bottom up by dropping or displacing progressively larger
actuating balls into the assembly, thereby allowing the operator to
selectively stimulate a plurality of producing zones in a single
trip.
Although the embodiments described above are actuated by using
successively larger balls, it should be readily understood that the
modules can be actuated by other means. For example, the shifting
sleeves of the modules could be easily adapted to be actuated by
dropping or pumping down the assembly appropriately sized darts,
bars, plugs, or the like. Alternatively, each shiftable sleeve may
include a selective profile, such as an Otis "X" or "R" style
profile, and the actruating means for a particular sleeve would
include a locking mechanism with a mating profile. In such an
embodiment, the actuating means would pass through all modules
except the module that had a shifting sleeve with a mating
profile.
FIG. 5 shows the process of cementing an assembly 1 into the open
wellbore 2. Cement 130 is pumped down a string 104 through the
plurality of modules 5, 10, 15, and 20 attached to the string 104.
A float collar 100 is connected to the centralizing coupling
connected to the lowermost module 20. Alternatively, the float
collar 100 may be connected directly to the lowermost module 20 or
a portion of the string 104 located below the lowermost module 20.
The cement 130 is pumped through a shoe joint 110 and float shoe
120 connected to the float collar 100. The cement 130 exits the
float shoe 120 and fills the annulus between the string 104 and the
open wellbore 2 to cement the string 104 within the open wellbore
2.
A wiper plug 140 is pumped down the string 104 above the trailing
end of the cement 130 being pumped down the string 104. The wiper
plug 140 wipes the string 104 removing cement 130 from the interior
of the string 104 and from the interior of the modules 5, 10, 15,
and 20. The wiper plug 140 is pumped to the end of the string 104
removing the cement 130 within the string 104 until it reaches the
float shoe 120. Alternatively, the wiper plug 140 may be landed in
the float collar 100. At least one wiper ball 150 may also be
pumped down the string 104 to remove any residual cement 130
remaining in the string 104 or in any of the modules 5, 10, 15, and
20. Multiple wiper balls 150 may be pumped down the string 104 in
an effort to wipe the string 104 and modules 5, 10, 15, and 20 of
any residual cement 130. The wiper ball 150 may be comprised of
natural rubber or other materials that allow the wiper ball to wipe
the string 104. Further, multiple wiper balls 150 having differing
outer diameters may be used to ensure the removal of residual
cement 130 as would be appreciated by one of ordinary skill in the
art having the benefit of this disclosure. The wiper ball 150 used
to wipe the string 104 and the modules 5, 10, 15, and 20 may be,
for example, a drill-pipe wiper ball comprised of natural
caoutchouc rubber commercially offered by Halliburton.
An acid solution 170, such as acetic acid, may then be pumped down
the string 104 to displace the cement 130 and the wiper plug 140
and wiper ball(s) 150. The acid solution 170 may prevent any
residual cement 130 from setting or curing within the string 104
and the modules 5, 10, 15, and 20. Further, the acid solution 170
may break up or fracture the cement 130 on the exterior of the
string 104 at the module locations when the stimulation process, as
discussed above, begins. The wiper ball 150 may be pumped down the
string 104 in a spacer fluid 160 between the cement 130 and the
acid solution 170 to help protect the wiper ball 150 from being
damaged by the acid solution 170. The acid solution 170 may be
pumped down the string 104 until the central passageway of each
module contains the acid solution 170. After the acid solution 170
has been pumped into and retained in the string 104, the operator
will allow the cement 130 on the exterior of the string 104 to cure
and cement the string 104 within the open wellbore 2. The presence
of the acid solution 170 within the string 104 during the curing
process may ensure that the slidable sleeves within the modules
function properly when actuated.
FIG. 6 illustrates the assembly 1 cemented in the open wellbore 2.
At this point, fluid may be pumped within the string 104 until the
hydraulic pressure moves the sliding sleeve of the lowermost module
5 to its open position. After the sleeve is in its open position,
the acid solution 170 will exit through the radial passageways and
begin to break down and remove the cement 130 that has formed
adjacent to the module. The fluid will then fracture the formation
once it has removed the cement at the zone of interest. The next
module will be actuated as discussed above and the process will be
repeated until each of the zones of interest has been
stimulated.
Although various embodiments have been shown and described, the
invention is not so limited and will be understood to include all
such modifications and variations as would be apparent to one
skilled in the art. Other numerous changes in the details of
construction and arrangement of parts will be readily apparent to
those skilled in the art and which are encompassed within the
spirit of the invention and the scope of the appended claims.
* * * * *